Lighting is primarily provided for people, not for the buildings or roadways or objects illuminated. Peoples’ needs should determine what kind of lighting is provided. Meeting those needs is important because a good visual environment is critical to health, productivity, comfort, aesthetics, safety, communication and mood. Lighting designers have an opportunity and responsibility to support and improve the quality of life for everyone.

Recently, lighting has become a subject of much greater interest than for many years. This is for three reasons:

The ageing of the population in many developed countries. As the human visual system ages, its capabilities deteriorate. Lighting can be used to help older people to see well and hence to live active lives for longer.

The need to reduce carbon emissions to minimize climate change. Lighting is a major user of electricity and the generation of electricity is a major source of carbon emissions. This means that lighting is under pressure to do more with less.

The recognition that exposure to light can have significant non-visual effects on human health. The potential for exposure to light to cause tissue damage has been known for many years, but now its influence on the human circadian system, which operates at a very basic level of human physiology, is also appreciated. The Health & Performance section includes a detailed conversation regarding the circadian system.

Taken together, these developments mean that the number of factors that should be considered when determining if a lighting installation is fit for purpose has increased. However, one factor that will almost always need to be considered is how well the lighting enables people to see. This is the topic of this chapter.